I know that Cordierite is a popular material for baking stones but don't have any specific advice on that material. I would call Sheffield and ask them the questions you posed. I would think that they have been asked those questions before.

Thanks Peter. I actually had seen that thread but did not come across any further information on cordierite. Most quarry tile users seem pretty enthusiastic about it. I know that some of the commercial ovens have cordierite decks so that's why I was interested in finding out. I'll give Sheffield a call and post what I can find out.

This was the reply I got from Sheffield:"you can cook on a new kiln shelf. The downside is that they are designed to be poor absorbers of heat so not as good as say a pizza stone however much more durable than a pizza stone. Pizza stones are cone 6 or cone 10 stoneware so what you could do is cover a kiln shelf with a slab of stoneware clay ...fire the whole thing in a kiln and then you would have the ultimate cooker... just a thought"

Probably because you don't want the bottom of the pizza to burn before the top is finished baking. The goal is to bake top and bottom at the same rate. However, the specific heat capacity of Cordierite is actually pretty high at 1.465 J/g °C-1, so although it conducts heat slowly, it can hold on to a lot of heat for its mass.

So, this material would take a long time to heat up, but once it heated up it would stay hot for awhile?

Rather than just saying it would take a long time to heat up, it might be useful to compare it to other well known materials. Stainless steel for instance, would heat up 5.4 times faster than Cordierite per the same amount of mass, but Cordierite has the capacity to hold 2.93 times more heat than stainless steel per the same amount of mass. Another ceramic, Alumina (Aluminum oxide), will heat up 11 times faster, but hold 1.94 times less heat. By comparison, Cordierite takes longer to heat up than these materials, but you have to consider that these materials transfer heat so quickly, you could end up burning the bottom of the pizza.

Based on its thermal properties, I don't see why it would take much longer than a normal pizza stone if it's of similar size and weight. If you tell me what temperature you want to bake at, I can tell you about how long it will take to heat up.

Just following up. Got a 15" x 15" x 5/8" kiln shelf from Sheffield Pottery made of Cordierite. I wasn't sure if I needed to do the outgassing thing or not so I did just to be safe. The only other thing that concerned me was there was a number labelled on it with blue ink. I tried sanding it off but it seemed to go deep into the substance of the stone itself. It's only on 1 side so I tried not to cook on that area (but accidentally did anyway).

Anyway, the pizza came out good. The oven took a lot longer to heat up than it used to with only my pampered chef stone. In this case I cooked on the cordierite and put the old stone on the shelf above.

Here is some pricing news for Sheffield Pottery's kiln shelves. Right now they are having an "overstock" sale on several of their shelves in sizes convenient for the home oven. I just picked up a 16" x 16" x 0.75" shelf for myself.

In preparation for using the cordierite shelf for baking a pizza on tomorrow, I carbonized the bottom by mopping it with sugar-water and heating it in the oven at 600°F for about an hour. This is to darken it for more rapid radiant heat absorption. I will likely sugar-heat treat it a few more times before all is said and done. I will only treat the shelf this way on the bottom, as I want the top to remain as reflective as possible to benefit the rim of the crust not in direct contact with the shelf. Attached is an image of the contrast resulting from the first treatment.

I just thought I would throw up an image or two of a pizza I baked tonight on the cordierite shelf. I have been baking on this shelf constantly since September 11, but I haven't stopped to take pictures of the products until tonight. Even tonight's picture taking was totally unplanned, so the images aren't really all that great due to a rushed setup. The pizza however was great. It simply had mozzarella cheese and baby portobello mushrooms (no sauce).

Thanks. The oven is set for 600°F, and the shelf hovers just above that after 40 minutes of preheating. This pizza was baked in about 3 minutes.

- red.november

EDIT: FYI, I didn't bother taking a picture of the bottom of the crust, so I rotated the pizza so that the part of the rim (cornicione) with the same coloration as the bottom directly faced the camera.

Thanks. The oven is set for 600°F, and the shelf hovers just above that after 40 minutes of preheating. This pizza was baked in about 3 minutes.

- red.november

EDIT: FYI, I didn't bother taking a picture of the bottom of the crust, so I rotated the pizza so that the part of the rim (cornicione) with the same coloration as the bottom directly faced the camera.

RN,

What is the optimal position for the shelf in the oven?I currently use a fibrament stone but I am looking at purchasing a Cordierite-mullite shelf for my oven from a local pottery supply. It comes in 3/4" & 1" thickness. I am thinking the 1" is much better. Do you have any data to compare the 2 thicknesses?

I would keep the Fibrament stone unless there was something wrong with it.

- red.november

There is nothing wrong with the fibrament stone except the size, it only 13". I just purchased an 18" x 18" Cordierite-mullite kiln shelf, unfortunately they discontinued the 1" thick so I had to buy the 3/4". They also had the SC kiln shelves, the store owner discouraged me from buying it due to its fragile nature.

They also had a great deal on round 16" x 1/2" pure cordierite @$19 each. I'm thinking that 2 of these on top of one another would be great on an LBE.

In preparation for using the cordierite shelf for baking a pizza on tomorrow, I carbonized the bottom by mopping it with sugar-water and heating it in the oven at 600°F for about an hour. This is to darken it for more rapid radiant heat absorption. I will likely sugar-heat treat it a few more times before all is said and done. I will only treat the shelf this way on the bottom, as I want the top to remain as reflective as possible to benefit the rim of the crust not in direct contact with the shelf. Attached is an image of the contrast resulting from the first treatment.

- red.november

Hello

It would be nice to have an accurate measure of the temperatures on the black coated face and on the other one.You want the top face white because you think it will reflect heat.But other factors need to be considered.Most of the heat could be transfered by convection or conduction.If the face is black it could also absorb more (heating more the stone) and irradiate more, depending on its temperature, or more precisely it will irradiate at a different wavelength.To summarize we need to know what's more important, reflectivity or emisivity.

I just thought I would throw up an image or two of a pizza I baked tonight on the cordierite shelf. I have been baking on this shelf constantly since September 11, but I haven't stopped to take pictures of the products until tonight. Even tonight's picture taking was totally unplanned, so the images aren't really all that great due to a rushed setup. The pizza however was great. It simply had mozzarella cheese and baby portobello mushrooms (no sauce).

- red.november

I know this is an old post, really old post but I love that spider web effect in the rim. Always love spider webbed effect in pizza rims. I know this is an old post but do you know what dough formulation you used?

It would be nice to have an accurate measure of the temperatures on the black coated face and on the other one.You want the top face white because you think it will reflect heat.But other factors need to be considered.Most of the heat could be transfered by convection or conduction.If the face is black it could also absorb more (heating more the stone) and irradiate more, depending on its temperature, or more precisely it will irradiate at a different wavelength.To summarize we need to know what's more important, reflectivity or emisivity.

Firstly, if you look through more of my posts you will notice I have talked quite a bit about carbonizing or seasoning the top. It was in this particular case I only wanted to carbonize the bottom. Secondly, there is no question that a darker surface will absorb heat more rapidly than a white or reflective surface, so I'm not sure why it matters what the temperatures are. Also, simply saying "temperature measurement" doesn't mean much anyway. Measured how, IR thermometer or thermistor? An IR thermometer will only measure radiation, and a thermistor will only measure conduction (assuming a silvery metallic probe).

Other factors need to be considered, indeed. Here are two of them. Metal conducts heat better than air or stone/ceramic, and a broiler element gets exponentially hotter than the stone. So if you aren't preheating your stone with a broiler element, and you aren't planning to preheat very long, or you use the broiler element during the bake, the top of your oven will be much hotter than the top of your stone. Depending on the preheat time and where the stone is placed, there is great potential for more thermal energy reaching the top of the stone via radiation from the top of the oven than from the stone itself. If you question this, just look at the top of your crust sometime. All that browning is a result involving convection and radiation; not conduction. Now look at the pockets that form on the bottom of the crust during baking, and take note of how pale they are. The surface of those pockets are only millimeters away from the stone surface. You have to realize that the pizza itself is a big heat sink. It's drawing so much energy from the stone via conduction, that the emission of radiation is diminished. So when you compare radiation from the stone versus radiation from a broiler element or preheated metal surface, the stone loses almost every time.

or more precisely it will irradiate at a different wavelength.

Wavelength and temperature are not related in the manner you suggest. Bodies emit radiation over a broad range of wavelengths. To understand the full relationship, read about the Stefan-Boltzmann Law and spectral radiancy. However, carbon is the main actor in all oven radiation no matter what surface we're talking about, so spectral radiancy is unlikely to change significantly in any case.